Summer humidity, dust allergy, and mold risk in a coastal apartment

Target humidity

For dust allergy, mold sensitivity, or a bedroom with previous mold, the practical indoor target is 40–50% relative humidity. Because mold previously appeared in the bedroom, the stricter end of the range is preferable: 45–50% most of the time.

Humidity above 60% is generally too high for this situation. It supports dust mites, makes mold growth more likely, and can keep bedding, furniture, walls, and stored fabrics slightly damp.

Apartment zones

The apartment should be treated as two main humidity zones:

• Bedroom suite: room 8, about 17.5 m², plus the attached bathroom 9.
• Living area: room 5, connected to the hall and served by the Daikin AC.

The bedroom suite needs priority because it is the sleeping area and because that room had mold a year ago. The living room can be managed partly by the Daikin AC when it is in DRY mode or when cooling is actually active.

Reading the current numbers

Sea air and humidity

Living about 300 metres from the sea does not change the indoor humidity target. It does make open-window drying less reliable. Coastal air often contains a lot of moisture, especially at night and in summer.

Relative humidity can be misleading because it depends on temperature. Dew point is usually a better indicator of how much moisture the outdoor air actually contains. If the outdoor dew point is high, opening windows can increase indoor moisture even when the apartment feels warm.

Electrolux dehumidifier setup

The unit considered here is the Electrolux EXD20DN4W, rated at 20 L/day, 440 W, with a 3 L tank, dust filter, and R290 refrigerant. It is adequate for targeted use, but because there is only one unit, placement matters.

Priority placement

The priority placement is bedroom 8, near but not blocking the bathroom entrance. Clear space around the air intake and outlet is important. The hygrometer should not sit directly in the dehumidifier airflow, near the bathroom doorway, or near a window.

SMD mode

Running it in SMD mode for 48–72 hours is reasonable for initial drying. SMD should regulate humidity automatically rather than running the compressor at full load every minute. If SMD stabilizes above 50–55%, manual humidity control at 50% is preferable.

Bathroom handling

1. Bathroom door closed during showers.
2. Direct outdoor ventilation through the bathroom window or extractor.
3. Bathroom window closed once visible steam and condensation are gone.
4. Bathroom door reopened after that so the dehumidifier can remove remaining moisture from the bedroom suite.

The bathroom window should not stay open continuously while the bedroom is being dehumidified. In Constanța summer conditions, that can feed humid air back into the suite.

Electricity use and cost

The 440 W rating is the approximate maximum load for the whole machine: compressor, fan, and electronics together. The fan alone is much smaller, probably only a few tens of watts, but the exact figure is not published for the unit.

The basic calculation is:

Those examples assume the compressor is actively drawing near 440 W for the whole period. In real use, once the room is dry, the compressor should cycle off. This means the daily consumption should fall after the first drying period.

At 70% versus 59%, the instantaneous power draw is not very different if the compressor is running. The savings come from runtime: at 59% the room is closer to the set point, so the compressor should reach cycling sooner.

Overnight humidity rise

A closed bedroom can climb back to 70% overnight when the dehumidifier is off. The causes are usually combined:

• Two people sleeping add moisture through breathing and perspiration.
• The closed bedroom door reduces air volume and airflow.
• The attached bathroom may leak humidity back into the bedroom, especially if towels, shower surfaces, or drains remain damp.
• If the room cools overnight, relative humidity rises even when the actual amount of water in the air does not change.
• Furniture, bedding, walls, and fabrics can release stored moisture after the dehumidifier is turned off.

When overnight operation is impractical

The unit can do more of the work before and after sleep:

1. Several hours of bedroom operation before bed, aiming for about 45%.
2. Bathroom window closed before dehumidifying.
3. Wet towels kept out of the bedroom suite overnight.
4. Bedroom door slightly open if privacy, noise, and comfort allow it.
5. Morning operation until the room returns to 45–50%.

The Daikin AC role

The Daikin AC in the living room is useful for room 5 and nearby circulation space. It will not reliably dehumidify bedroom 8 while the bedroom door is closed.

At 26°C room temperature, the AC may not dehumidify much if set to COOL at 26°C because the compressor may barely run. For humidity reduction, the useful modes are:

• DRY mode when the living room is humid but not too hot.
• COOL mode at 25–26°C only if it actually runs long enough to remove moisture.
• Not FAN mode, because fan-only operation moves air but does not remove water from it.

During AC or dehumidifier operation, exterior windows and balcony doors should remain closed.

What the Xiaomi air purifiers handle

The two Xiaomi Pro air purifiers can help reduce airborne particles such as dust and some allergens, assuming the filters are maintained and the units are positioned with clear airflow.

However, air purifiers do not lower humidity, dry damp materials, stop condensation, or fix mold growth. They are supplementary; the core mold-control intervention is moisture control.

Daily routine

Morning

• Bedroom humidity check before opening windows.
• Electrolux operation in bedroom 8 until the independent hygrometer reads 45–50%.
• Shower surfaces dry; wet towels removed from the bedroom suite.

Daytime

• Windows closed while dehumidifying.
• Daikin DRY mode if living-room humidity stays above 60%.
• Dehumidifier moved to the living room only when the bedroom is stable.

Before bed

• Several hours of bedroom dehumidification.
• About 45% relative humidity to create an overnight buffer.
• Bathroom window closed and bathroom kept as dry as practical.
• Bedroom door slightly open if the rest of the apartment is drier.

After showers

• Bathroom door closed during the shower.
• Direct outdoor ventilation until visible steam and condensation clear.
• Bathroom window closed before dehumidifying the bedroom suite.

When to look deeper

If the room is pre-dried to 45–50% but repeatedly returns to 70%, or if the dehumidifier cannot bring the bedroom below 55–60% after several days, the issue may not be just ordinary summer humidity.

Items worth checking:

• Condensation on windows, corners, or exterior walls.
• Musty smell in the bedroom, bathroom, wardrobes, or behind furniture.
• Recurring marks where the previous mold appeared.
• Dampness behind the bed, wardrobes, curtains, and along exterior-wall corners.
• Bathroom leaks around the shower, toilet, sink, drains, or wall penetrations.
• Indoor clothes drying, wet towels, many plants, or blocked airflow behind furniture.

Because the bedroom previously had mold, an airflow gap behind large furniture on exterior walls and regular inspection of the old affected area are both useful.